The present invention relates to a digital automatic gain control circuit.
As is well known, "automatic gain control" (AGC) is a function for maintaining a certain constant input level by smoothing out variations. Conventionally, the AGC function is achieved by means of an analog circuit such as an operational amplifier. However, recent progress in digital processing techniques has made it possible to achieve an AGC function by means of a digital circuit. Such a digital AGC circuit has already been proposed in, for example, Japanese Unexamined Patent Publication No. 50-45506 (1975).
In the digital AGC circuit, signals, appearing at each portion along an AGC loop thereof, can be obtained through digital arithmetic operations. Execution of the digital arithmetic operations by a high capacity processor has easily made possible high-speed operation which is impossible with conventional analog AGC circuits.
While such high-speed operation digital AGC circuits are now being used, they are still not always fast enough for the operation speed of high-speed operation systems such as data modems.